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Abstract The Mn valence in thin film La0.7Sr0.3MnO3 was studied as a function of film thickness in the range of 1–16 unit cells with a combination of non-destructive bulk and surface sensitive X-ray absorption spectroscopy techniques. Using a layer-by-layer valence model, it was found that while the bulk averaged valence hovers around its expected value of 3.3, a significant deviation occurs within several unit cells of the surface and interface. These results were supported by first principles calculations. The surface valence increases to up to Mn3.7+, whereas the interface valence reduces down to Mn2.5+. The change in valence from the expected bulk value is consistent with charge redistribution due to the polar discontinuity at the film-substrate interface. The comparison with theory employed here illustrates how this layer-by-layer valence evolves with film thickness and allows for a deeper understanding of the microscopic mechanisms at play in this effect. These results offer insight on how the two-dimensional electron gas is created in thin film oxide alloys and how the magnetic ordering is reduced with dimensionality.

The interface of γ-Fe 2 O 3 /MgO(001) film have revived considerable attention. Polar catastrophe at the interface of γ-Fe 2 O 3 /MgO(001) film was investigated and an attempt to investigate the interface structure and growth mode of γ-Fe 2 O 3 /MgO(001) was given. The results show that the stoichiometric γ-Fe 2 O 3 with tetragonal space group of P4 1 2 1 2 should grow on MgO(001) in the [100] or [010] direction. The charge compensation by modifying the stoichiometry in the interface layer can not only stabilize the polar surface, but also give a reasonable interpretation for why the saturation magnetization (Ms) values of the very thin γ-Fe 2 O 3 /MgO films are larger than the bulk value of γ-Fe 2 O 3 in experimental studies. This study may widen the application of maghemite especially the γ-Fe 2 O 3 /MgO film. [ABSTRACT FROM AUTHOR]

While heterostructures are ubiquitous tools enabling new physics and device functionalities, the palette of available materials has never been richer. Combinations of two emerging material classes, two-dimensional materials and topological materials, are particularly promising because of the wide range of possible permutations that are easily accessible. Individually, both graphene and Pb 1-x Sn x Te (PST) are widely investigated for spintronic applications because graphene's high carrier mobility and PST's topologically protected surface states are attractive platforms for spin transport. Here, we combine monolayer graphene with PST and demonstrate a hybrid system with properties enhanced relative to the constituent parts. Using magnetotransport measurements, we find carrier mobilities up to 20 000 cm 2 /(V s) and a magnetoresistance approaching 100%, greater than either material prior to stacking. We also establish that there are two distinct transport channels and determine a lower bound on the spin relaxation time of 4.5 ps. The results can be explained using the polar catastrophe model, whereby a high mobility interface state results from a reconfiguration of charge due to a polar/nonpolar interface interaction. Our results suggest that proximity induced interface states with hybrid properties can be added to the still growing list of behaviors in these materials.

The relative significance of quantum conductivity correction and magnetic nature of electrons in understanding the intriguing low-temperature resistivity minimum and negative magnetoresistance (MR) of the two-dimensional electron gas at LaAlO 3 /SrTiO 3 interfaces has been a long outstanding issue since its discovery. Here we report a comparative magnetotransport study on amorphous and oxygen-annealed crystalline LaAlO 3 /SrTiO 3 heterostructures at a relatively high-temperature range, where the orbital scattering is largely suppressed by thermal fluctuations. Despite of a predominantly negative out-of-plane MR effect for both, the magnetotransport is isotropic for amorphous LaAlO 3 /SrTiO 3 while strongly anisotropic and well falls into a two-dimensional quantum correction frame for annealed crystalline LaAlO 3 /SrTiO 3 . These results clearly indicate that a large portion of electrons from oxygen vacancies are localized at low temperatures, serving as magnetic centers, while the electrons from the polar field are only weakly localized due to constructive interference between time-reversed electron paths in the clean limit and no signature of magnetic nature is visible., (© 2021 IOP Publishing Ltd.)